Microscopic analysis of single-fiber push-out tests on ceramic matrix composites performed with Berkovich and flat-end indenter and evaluation of interfacial fracture toughness

Single-fiber push-out tests performed with a Berkovich and a flat-end indenter tip were conducted on the same SiC/PyC/SiC ceramic matrix composite sample for comparison. Push-out measurements were stopped at different stages during the experiment for a detailed microscopic analysis of the front and back side of the sample, to investigate the progression of failure during push-out process. The microscopic analyses reveal differences from the established interpretations which are crucial for quantitative evaluation of interface properties. Based on the microscopic findings, a modified loading schedule comprising unloading–reloading cycles is proposed, which provides access to the dissipative and non-dissipative energy contributions during push-out test. A new energy-based approach is presented which allows for the determination of the interfacial fracture toughness, without assumptions regarding the stress distribution along the interface to be made. Presuming stable crack growth along the complete debonding length, the interfacial fracture toughness of the sample investigated amounts to 44 ± 9 J/m2.